Preparation Of Graphene-based Nanocomposites And Their Influence On The Thermal Conductivity Of Polymers

Electronic devices play an important role in our daily life.Considering their great contribution in various fields,they were expected to play a greater role in the future.At present,with the rapid development of information society,various semiconductor devices were developing towards the direction of miniaturization and integration of power density.However,the resulting inevitable high temperature would seriously impact the performance of electronic equipment,and even irreversibly damage electronic components.Therefore,heat dissipation is now a major research area for scientists in the design and preparation of modern microelectronic materials to fully maintain their efficiency and maximize their service life.Although the polymer materials have the advantages of high specific strength and modulus,light weight,corrosion resistance and easy processing,their thermal conduction and heat dissipation in electronic devices is limited because of their low thermal conductivity.Researchers achieve this goal by compounding thermal conductive fillers with polymer.Among many thermal conductivity fillers,graphene,boron nitride and other graphene-like nanomaterials are considered to be very ideal fillers due to their excellent thermal conductivity,resistance to acid and alkali corrosion,and high temperature stability.Studies show that the dispersion of graphene-like nanofillers into the polymer matrix could significantly improve the thermal conductivity of the polymer.However,the agglomerate of fillers in the polymer matrix often affects the heat transfer rate of the polymer composites,which make the thermal conductivity of the polymer matrix composites could not be effectively enhanced.Therefore,it has great significance to explore different ways to disperse nanofillers evenly into the polymer matrix.In this paper,the thermal conductivity of polymer based composites were enhanced by constructing three-dimensional graphene network,graphene-metal hybrid and surface modification of boron nitride for improving their dispersion in polymer matrix.Specific research contents were as follows:1.Graphene oxide was prepared by Hummer's method,then the RGO-PU with three-dimensional network was fabricated through one step hydrothermal reduction and freeze-drying by using PU sponge as a template and GO as a precursor.Then liquid polysulfide rubber(LPO)was used as polymer matrix and introduced into three-dimensional graphene network(RGO-PU)by vacuum impregnation to prepare polysulfide rubber composites(RGO-PU/PSR).Compared with pure polysulfide rubber,the thermal conductivity of RGO-PU/PSR composites is significantly improved.For example,the thermal conductivity of RGO-PU/PSR composites reach0.598 W/(m·K),which have increased by 153% compared with that of pure PSR.The volume resistivity test results show that the volume resistivity of 0.5 wt%RGO-PU/PSR composite is 2.6×106 ?·cm,Compared with the pure PSR,the volume resistivity has a conspicuous 5 orders of magnitude decrease.In addition,the compression results showed that the compression strength and Young's modulus of RGO-PU/PSR composites are higher than those of pure PSR.2.Graphene-silver nanocomposites were prepared by in situ reduction method.Then GNs-Ag/HTPB composites was prepared by dispersing graphene-silver hybrid into the polyurethane produced by the reaction of hydroxy-terminated polybutadiene(HTPB)and toluene diisocyanate(TDI)as curing agent.The structures of graphene and graphene-silver were analyzed by several characterizations,which showed that the silver nanoparticles were successfully reduced and the graphene-silver nanocomposites was prepared.As can be seen from the thermal conductivity results,0.5 wt% GNs-Ag/HTPB composites have the largest thermal conductivity,which is higher 52.6% than pure HTPB.In addition,the infrared thermal imaging results prove that the surface temperature of the GNs-Ag/HTPB composites rises faster than that of pure HTPB,indicating the capacity of heat dissipation was stronger.3.Firstly,boron nitride nanosheets were obtained by mechanical stripping.Then KH550 was used to modified boron nitride nanosheets.In addition,BN-CNTs hybrid was prepared by mixing carbon nanotubes with modified boron nitride.BN-CNTs composites as thermal filler was added into epoxy resin matrix to obtain Epoxy/BN-CNTs composites by mechanical stirring.As a contrast,the same content of BN,CNTs were dispersed to epoxy resin to form composites.A series of analysis and tests were carried out on the prepared composites.It is found that the Epoxy/BN-CNTs composites exhibit better thermal conductivity and mechanical properties than the neat Epoxy,Epoxy/BN and Epoxy/CNTs composites.